Here is a crash course introduction to frequency separation in Adobe Photoshop.
Frequency Separation sounds complicated, and most people do tend to over complicate it. But don’t let the name intimidate you. Frequency Separation is merely a Photoshop technique used to separate a person’s skin texture from their skin tones and blemishes onto separate layers. Now the benefit of that is that you’re able to retouch skin blemishes and still retain natural textures so that somebody doesn’t look like a porcelain doll. Now before you begin, it is worth mentioning that there is a free photoshop action available for frequency separation in the store in the event you just don’t feel like learning how to do it manually which is just fine.
Now, let’s just jump straight into Photoshop with the portrait that has already been specifically taken for this tutorial. In photoshop, you can zoom in and see the natural blemishes you want to remove from the face, however you can also see the pores which you don’t want to remove. The technique for frequency separation can easily be overused – in this instance you are using it specifically for individuals like portrait clients. This isn’t for an advertisement so you’re not aiming for perfect flawless skin, but what you’re trying to do is remove some of the major blemishes that are in the face. With that being said you can take this as far as that with this technique.
So what you what to do firstly is make two copies of the background layer and re-label them, again what you’re changing is creating two independent layers – separating the details and textures in one layer. Then you will go ahead and put the skin, the colour and the blemishes on the other layer. So the bottom layer you’re going to go ahead and label colour. The layer above it that contains the details will be named texture respectively. Keep in mind this is a formula, not theory so different images will often require a tweak to the treatment.
Now, hide the top layer (texture), then select your colour layer and go to Filter in the top toolbar, scroll down to Blur, Gaussian Blur. You will want to blur the skin enough so that you don’t have skin texture but not so much as to lose the structure of the image. What that means is, you can still see the nose, the eyes and shape of the face but no longer see pores. With this image 2.3 works however with your image it may be less or more depending what you’re trying to do.
Then you want to go ahead and unhide the texture layer then go to up to Image in your top toolbar and select Apply Image – go ahead and select a layer, make sure you’re selecting the colour layer, the bottom layer underneath. Then you want to change your blending mode to Subtract, change the Scale to 2, Offset to 128. Why? This is an algorithm that was created by someone else and has since been used by others within the industry. Of course then press okay. What you will now notice is it looks like a matte grey layer but if you zoom in you will see all the textures are still retained in their own independent layer. Now if you go ahead and hide the background layer you will see the difference. Hide the texture layer you will see the blurred layer. Essentially it is almost like running a High Pass layer. Now go ahead and select the top layer (Texture) and change the blending mode to Linear Light. What this will do is blend the two together on their own independent layers essentially looking like we’ve done nothing at all. Now that whole process, again is available as an action in the shop so you never have to do it manually ever again.
So now going forward any changes you want to make to the colour of the skin or the blemishes you will do from the colour layer. From here you can choose a variety of tools to correct the colour, in this case the patch tool is a preference as will allow for you to drag and drop colours to your liking depending on what you are trying to find. AS you move around the image and replace information over the areas that are off in colour or are small colour differences you will come across skin blemishes such as pimples which will require manipulation to both the colour and texture layer. The reason for this is the detail from the blemish will still be retained on the texture layer. So first correct the redness by using the patch tool on the colour layer then on the texture layer also use the patch tool and find another area of texture that is smooth or would better cover the area. By doing this you are just referencing the information from around the area, not blurring it. Do not forget to reference to the original now and then, you can do this by simply selecting and hiding the background layer to quickly toggle and see the progress.
One more quick trick while you’re here is airbrush the skin only slightly nothing crazy. So generate a new layer between the colour and texture layer, then using the Eyedropper Tool select a lighter colour in the area of the skin that you’re about to airbrush and paint over the area, if you’ve gone overboard you have a few options: you can control/undo or lower the opacity on that layer. Also use this if you want to remove some larger red areas such as on the nose by selecting a colour adjacent to the area but more beige in tone and not red as that is what you’re trying to remove. Again the goal here if you’ve executed correctly is to still see pores & texture. This is your key for great delivery to your average portrait client, not for advertising purposes.